Three Babesia species in Ixodes ricinus ticks from migratory birds in Sweden

Abstract

Background Migratory birds can cross geographical and environmental barriers and are thereby able to facilitate transmission of tick-borne pathogens both as carriers of infected ticks and as reservoirs of pathogenic microorganisms. Ixodes ricinus is one of the most abundant tick species in the Northern Hemisphere and a main vector of several Babesia species, some which pose a potential threat to human and animal health. At present only two cases of overt babesiosis in humans have so far been reported in Sweden. To better understand the potential role of birds as disseminators of zoonotic Babesia protozoan parasites, we investigated the presence of Babesia species in ticks removed from migratory birds. Methods Ticks were collected from birds captured at Ottenby Bird Observatory, south-eastern Sweden, from March to November 2009. Ticks were molecularly identified to species, and morphologically to developmental stage, and the presence of Babesia protozoan parasites was determined by real-time PCR. Results In total, 4601 migratory birds of 65 species were examined for tick infestation. Ticks removed from these birds have previously been investigated for the presence of Borrelia bacteria and the tick-borne encephalitis virus. In the present study, a total of 1102 ticks were available for molecular analysis of Babesia protozoan parasites. We found that 2.4% of the ticks examined, all I. ricinus, were positive for mammal-associated Babesia species. Out of all Babesia-positive samples, Babesia venatorum was the most prevalent (58%) species, followed by Babesia microti (38%) and Babesia capreoli (4.0%). B. venatorum and B. capreoli were detected in I. ricinus larvae, whereas B. microti was only present in I. ricinus nymphs. This supports the view that the two first-mentioned species are vertically (transovarially) transmitted in the tick population, in contrast to B. microti. The largest number of Babesia-infected ticks was removed from the common redstart (Phoenicurus phoenicurus) and European robin (Erithacus rubecula). Conclusions This study reveals that Babesia protozoan parasites are present in ticks infesting migratory birds in south-eastern Sweden, which could potentially lead to the dissemination of these tick-borne microorganisms into new areas, thus posing a threat to humans and other mammals.

Ornithological and molecular evidence of a reproducingHyalomma rufipespopulation under continental climate in Europe

“…Obviously, not all ticks carried by migratory birds in the spring were imported by them from southern countries, and this is particularly relevant to those avian hosts which arrive from their wintering grounds during the activity peak of local tick populations. Similarly to previous bird tick studies in the Carpathian Basin [26] and most countries north of the Mediterranean Basin (e.g., [27]), I. ricinus was the tick species most commonly collected from birds in 2022 in Hungary. Haemaphysalis concinna was the second most abundant tick species on birds, which, however, seems to be unique to the Carpathian Basin and its region [32].…”

“…In Hungary, studies on tick-infestations of birds date back to more than half a century [16], and have been ever since extensively performed on annual or tri-annual bases focusing on the same ringing station in the north-central part of the country (Ócsa: [24–26]). Similar reports on ticks from avian hosts are available from numerous European countries, as exemplified by Sweden [27], The Netherlands and Belgium [28], Germany [29] or Italy [30]. Relevant studies have also been reviewed recently [31,32].…”

Potential Role of Avian Populations in the Epidemiology of Rickettsia spp. and Babesia spp.

“…The same piroplasm species along with B. venatorum, was identified in ticks on Passeriformes from Latvia [94]. B. venatorum DNA has been identified in nymphs carried by Turdus philomelos in Northwestern Russia [95] and in Norway by passerine birds [78], while B. microti and B. venatorum infected both larval and nymphal stages of I. ricinus from Sweden [96]. Furthermore, DNA of B. microti was detected in Ixodes granulatus found on Emberiza spadocephala in Taiwan [97].…”

Ticks, Human Babesiosis and Climate Change

“…Some of these ticks may be infected with B. microti, but it is likely that dispersal by migratory birds is inefficient for B. microti, because this pathogen is not transmitted vertically by ticks (transovarial transmission) [30], and birds have, as yet, not been confirmed as reservoirs. As any larvae feeding on migratory birds would not be infected before or during their dispersal by birds, the only infected ticks that birds might carry would be nymphs infected as larvae on small mammal reservoir hosts, as demonstrated by the study of Wilhelmsson et al [52]. Adult female ticks arising from such nymphs are likely to feed on deer rather than B. microti reservoir hosts and would pose little zoonotic risk since they would probably be free of infection following their second moult [30].…”